linux-kernel - Re: [patch 0/3] x86/fpu: Prevent FPU state corruption

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Date:   Wed, 18 May 2022 13:18:58 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Vadim Galitsin <vadim.galitsyn@...cle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Filipe Manana <fdmanana@...e.com>
Subject: Re: [patch 0/3] x86/fpu: Prevent FPU state corruption

On Wed, May 18, 2022 at 01:14:40PM +0200, Jason A. Donenfeld wrote:
> I wrote a tiny reproducer that should be pretty reliable for testing
> this, attached below. I think this proves my working theory. Run this in
> a VirtualBox VM, and then move your mouse around or hit the keyboard, or
> do something that triggers the add_{input,disk}_randomness() path from a
> hardirq handler. On my laptop, for example, the trackpoint goes via
> hardirq, but the touchpad does not. As soon as I move the trackpoint
> around, the below program prints "XSAVE is borked!".

I should also add that the VM should have as many CPUs as the host, to
better the chances that the irq arrives on the same CPU that the guest
VM is running on.